1. Field of the Invention
The present invention relates to an electron emitting device, an electron source, an image display device, and methods of manufacturing these devices.
2. Description of the Related Art
Conventional electron emitting devices are roughly of two types, including thermionic-cathode electron-emitting devices, and cold-cathode electron-emitting devices. Example of cold-cathode electron-emitting devices include a field emission type (referred to as “FE type” hereinafter), a metal/insulator/metal type (referred to as “MIM type” hereinafter), a surface conduction type, and the like, types of electron-emitting devices.
Known examples of FE type devices are disclosed in M. P. Dyke & W. W. Dolan, “Field Emission”, Advance in Electron Physics, 8, 89 (1956), C. A. Spindt, “Physical Properties of Thin-Film Field Emission Cathodes with Molybdenum Cones”, J. Appl. Phys., 47, 5248 (1976), and Japanese Patent Laid-Open No. 3-46729.
Known examples of MIM type devices are disclosed in C. A. Mead, “Operation of Tunnel-Emission Devices”, J. Apply. Phys., 32, 646 (1961), etc.
Examples of surface conduction electron-emitting devices are disclosed in M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965), Japanese Patent Laid-Open Nos. 7-235255, 8-102247, 8-273523, 9-102267, and 2000-231872, and Japanese Patent Application Nos. 2836015 and 2903295.
A surface conduction type of electron-emitting device uses the phenomenon that an electric current is caused to flow through a small-area thin film formed on a substrate in parallel with the film plane to emit electrons. As the surface conduction type of electron-emitting device, a device comprising a SnO2 thin film by Elinson, a device comprising an Au thin film (G. Dittmer: “Thin Solid Films”, 9, 317 (1972)), a device comprising an In2O3/SnO2 thin film (M. Hartwell and C. G. Fonstad: “IEEE Trans. EDConf.” 519 (1975)), and a device comprising a carbon thin film (Hisashi Araki, et al: “Shinku” (Vacuum), Vol. 26, No. 1, p. 22 (1983)) are known.
An electron source substrate comprising a plurality of the above-described electron-emitting devices can be combined with an image forming member comprising a fluorescent material or the like to obtain an image forming apparatus.
However, in the surface conduction type of electron-emitting devices, stable electron emission performance and electron emission efficiency are not necessarily obtained. Therefore, at present, it can be difficult to provide an image forming apparatus having high accuracy and excellent operation stability by using surface conduction type electron-emitting devices.
Therefore, as disclosed in Japanese Patent Laid-Open Nos. 7-235255, 8-264112, and 8-321254, a device subjected to a “forming step” may be subjected to a treatment called an “activation step”. The “activation step” represents a step of significantly changing a device current If and an emission current Ie.
Like the “forming step”, the “activation step” can be performed by repeatedly applying a pulse voltage to the device in an atmosphere containing an organic material. In this step, carbon or a carbon compound is deposited in the gaps and near the gaps formed in the “forming step” from the organic material present in the atmosphere. Consequently, the device current If and the emission current Ie are significantly changed to obtain higher electron emission performance. Furthermore, Japanese Patent Laid-Open No. 8-321254 discloses another method for improving the electron emission performance by a step different from the “activation step” disclosed in the above publications.
FIGS. 40A and 40B schematically show the general construction of a surface conduction type of electron-emitting device formed by the “activation step” disclosed in the above publications. FIGS. 40A and 40B are respectively a plan view and a sectional view of the electron-emitting device disclosed in the above publications.
In FIGS. 40A and 40B, reference numeral 131 denotes a substrate, reference numerals 132 and 133 denote a pair of electrodes (device electrodes), reference numeral 134 denotes a conductive film, reference numeral 135 (FIG. 40B) denotes a second gap, reference numeral 136 denotes a carbon film, and reference numeral 137 denotes a first gap.
FIG. 41 consisting of FIGS. 41A to 41D schematically shows an example of a process for forming an electron emitting device having the structure shown in FIGS. 40A and 40B.
First, the pair of electrodes 132 and 133 is formed on the substrate 131 (FIG. 41A).
Then, the conductive film 134 is formed for connecting the electrodes 132 and 133 (FIG. 41B).
Then, in a “forming step”, a current is passed between the electrodes 132 and 133 to form the second gap 135 in the conductive film 134 (FIG. 41C).
Furthermore, in an “activation step”, a voltage is applied across the electrodes 132 and 133 in a carbon compound atmosphere to form the carbon film 136 within the gap 135 on the substrate 131 and on the conductive film 134 near the gap 135, to form the electron-emitting device (FIG. 41D).
On the other hand, Japanese Patent Laid-Open No. 9-237571 discloses a method of manufacturing an electron-emitting device. The method comprises a step of coating an organic material such as a thermosetting resin, or the like on a conductive film and a step of carbonizing the coating, instead of the “activation step” in which a pulse voltage is repeatedly applied between electrodes in an atmosphere containing an organic material to deposit carbon and/or a carbon compound on a device.